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Link G4 strange fuel issues

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Hi guys,

I have a really strange issue with my Link G4 plugin board for my V6 WRX STI.  I have no overrun fuel cut enabled at all, however on light throttle usually going down hill, the AFR's max out at 20.9 on my wideband gauge.  I did some logging and can see the injector actual pulsewidth change from around 2.3ms at 2800rpm, -50kPa MGP pressure with a value of 39% for the fuel table, then as I lift my foot off, I have a fuel table value of 43% at 2800rpm and -70kPa vacuum however I see the actual pulsewidth decrease from 2.3ms down to 1.75 then finally to 1.4.... as the rpm's drop because I am slowing down, the pulsewidth remains small until I put my foot back down again.. I've attached some screenshots to show the issue.  Is there something I have set wrong in my tune or is this expected behaviour? 

You can see in the XY Plot 2 at the bottom left of the screenshots, the real lean areas when I have light throttle. I've attached my pcl tune I am using as well. 

Cheers, Mike

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log2.png

Link G4 1000cc injectors - Adjust injector timing.pcl

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That all looks fairly normal and as expected to me.  There is not going to be much combustion happening when the throttle is closed so there will be excess oxygen in the exhaust gas.

The reduction in pulse width as MAP goes lower is due to the standard "MAP compensation" that is part of the fuel equation.  

Edited by Adamw

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Yeah it's odd though because it only happens below 2500rpm down till around 1100rpm.  The idle pulsewidth is 1.8ms and the pulsewidth I observed logging at these rpm's remained at 1.3ms on light throttle downhill - surely it can't be less than the idle pulsewidth? Above 2500rpm and it's perfect with no lean spots.  

Cheers, Mike

screenie.png

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  The idle pulsewidth is 1.8ms and the pulsewidth I observed logging at these rpm's remained at 1.3ms on light throttle downhill - surely it can't be less than the idle pulsewidth?

From that scatter plot above it looks like your MAP at idle is about 40KPa, in the overrun areas at 1700-2500RPM MAP drops down to about 22-25KPa.  Since the MAP has reduced by about 35%, then the ECU will try to reduce the pulsewidth by 35%.  That doesnt quite tally with your 1.8 Vs 1.3ms but remember there are fuel table numbers and deadtimes etc influencing that as well.  So yes, the pulsewidth reducing below normal idle pulsewidth during overrun is normal and expected. 

So what are you actually worried about?  Lean displayed AFR on overrun?

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Ahh that makes sense yeah, basically the issue is that it's really lean on light throttle, or when it's going downhill with my foot off it's pegged at 22.9 AFR so when I get back onto the throttle again it sometimes is fairly jerky.  I've had a bit of a play around with the tip in enrichment and it seemed to help a little bit but still not the best on light throttles.  Do you recon I should be checking for vacuum leaks?

 

Cheers, Mike

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Adam could raising them minimum effective pulse width help in this situation?

There is no "minimum pulsewidth" function in the G4 from memory.  

Mike, if you post you map and log I will take a look.  I would like to see what ign timing etc is doing in the "jerky" area.

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